Generators for exciting piezoelectric transducers may be used, for example, to diffuse a fragrant substance, for example, a perfume. In some instances, the transducer may be excited at a particular frequency where it is desired to obtain a suitable energy efficiency. This may be particularly useful when the generator is powered by an energy source, such as a battery or a rechargeable battery, from which it is desired to minimize the power consumption.
By way of example, the frequency may be a resonant frequency or an anti-resonant frequency, and it can vary as a function of various operating parameters, such as, for example, temperature, aperture size associated with a diaphragm, and/or the rheological characteristics of the liquid to be atomized.
It is thus known to seek to servo-control the excitation of frequency of the transducer by measuring an electrical magnitude associated with its operation, so as to keep the excitation frequency as close as possible to the optimum frequency.
Atomizer devices including a relatively complex analog circuit for servo-controlling the excitation frequency are known from U.S. Pat. No. 3,904,896 and Japanese patent document No. 06-254 455.
U.S. Pat. No. 4,689,515, European patent document No. 0 123 277, and U.S. Application Publication No. 2002/0129813 describe atomizer devices including digital processor units that respond to variation in an electrical magnitude associated with the operation of the transducer in order to keep the excitation frequency at an optimum value.
International publication No. WO 00/51747 describes an atomizer device in which the excitation frequency of the transducer varies as a saw tooth over a predefined frequency band while the excitation voltage decreases exponentially.
French patent application FR 2 802 836 describes another atomizer device. During an initial stage, a search is made for an optimum excitation frequency. This search is performed initially by sweeping through a relatively broad frequency band extending from 1.7 megahertz (MHz) to 1.9 MHz, with a frequency step-size of 10 kilohertz (kHz). The frequency is determined by analyzing the magnitude of the excitation current. Once the frequency value has been determined, a frequency sweep is performed using a step-size of 1 kHz to determine the optimum excitation frequency more accurately, using the same criterion. Thereafter, during a subsequent stage of operation, excitation is performed at the determined frequency, except when certain characteristics of the excitation current exceeds predefined limit values. It can be difficult to measure the value of the excitation current.
Therefore, it may be beneficial to further improve generators for atomizer devices so as to benefit from an atomizer device that presents characteristics that are satisfactory in terms of atomization and in terms of power consumption, while still being relatively inexpensive to fabricate. Further, benefits may be obtained from a generator for an atomizer device in which the transducer is excited in such a manner as to extend its lifetime.
The invention may satisfy some or all of these needs.